Fetch a model with options unless it has an attribute. Return promise and resolve with instance so you can easily feed it further into your controllers.

model.js.coffee

class Model extends Backbone.Model
  fetchUnless: (key, options = {}) ->
    defer = $.Deferred()

    if @has(key) 
      defer.resolve(@)
    else
      @fetch(options).done =>
        defer.resolve(@)

    defer.promise()